Seamless cans made from a metal such as aluminum or steel have large shock resistance and do not permit gases such as oxygen to pass through, offer such advantages as far superior preservability of the contents to the plastic containers as well as small weight as compared to glass bottles, and have been widely used as containers for containing carbonated beverages, alcohol beverages and many other beverages and foods.
Trade names and a variety of designs have been printed on the outer surfaces of the seamless cans by the plate-type printing using a printing plate, such as offset printing (patent document 1), or by the ink-jet printing without using the printing plate (patent document 2).
The ink-jet printing requires no plate offering such advantages that the design to be printed can be freely changed in short periods of time (variableness), that the ink can be thickly printed enabling images with deepness to be formed and that highly fine images such as photographs can be excellently reproduced.
On the other hand, printing images onto the outer surfaces of the seamless cans is of such a nature that the images are printed on the curved surfaces of cylinders made from a non-absorptive material that does not absorb the printing ink, the printing being effected while rotating the seamless cans. Therefore, if the printing ink of a low viscosity is used, the ink flows and spreads immediately after being printed forming blurred images and making it difficult to obtain sharply printed images. To ink-jet print the images onto the non-absorptive cylindrical containers such as seamless cans, therefore, it is a generally accepted practice to use an ultraviolet ray-curing ink that is capable of being cured or half-cured immediately after it is ejected and has impinged (patent document 3).